Anyone skilled in the art of glass container manufacture is familiar with the individual section machine in which a number of machine sections are mounted side-by-side on a single machine bed to operate in synchronization with each other while being independently adjustable. In the utilization of a press and blow method of glass container production in such a machine, discrete molten glass gobs are fed into an upwardly-open blank mold after which the mold is closed at the top by a baffle. Although a single gob mold may be utilized, it is more common to have a plurality of molds in a section, such as double gob or triple gob arrangements. Then, separate molten glass gobs are fed simultaneously to each mold in the section.
For each mold, a vertically-elongated pressing plunger is driven upwardly to press the molten glass into the blank mold and into an adjacent neck ring mold, forming a parison from the glass gob. The plunger is then retracted and the blank mold and the baffle are temporarily removed so that the parison can be inverted by the neck ring mold from the blank to a laterally adjacent blow mold station where the final formation of the glass container occurs by a blowing operation.
For each blank mold, there is a separate mechanism for supporting and driving a pressing plunger for initially forming the parison in cooperation with the mold, and this mechanism includes a vertically-elongated cylinder casing mounted to support an axially-oriented piston rod within the casing. The pressing plunger is removably mounted to the upper end of the piston rod whereby it can be cycled through its pressing operation by linear reciprocation of the piston rod.
Pressurized air is directed into the cylinder casing and upwardly against an annular base of the piston to cause it to move vertically, and means is provided to reverse the air pressurization within the casing to retract the piston during the timed pressing cycle. A separate pressurized air flow is provided to the mechanism for the purpose of plunger cooling. Typically, the cooling air flow enters through a port in the base or end cap of the cylinder and is directed centrally upwardly through a fixed air tube which projects from the base end of the cylinder and coaxially upwardly. The upper end of the air tube projects into a central bore in the piston rod which is in air flow communication with the hollow plunger on the piston rod portion's upper end.
A problem frequently encountered in the operation of the type of machine heretofore described is air leakage between the cooling air conduit or passageway to the plunger and the main chamber of the cylinder. Such leakage negatively affects the air pressure in the cylinder which determines the motion and position of the plunger. During a press and blow cycle, it is required that the plunger move through three successive positions: an invert-maximum down position; an intermediate or loading position when the glass gob is being loaded into the blank; and the pressing position when the gob is formed into the parison. The intermediate position must be held during the entire loading operation, without plunger drift, however, a cooling air leak into the main body of the cylinder can result in plunger drift or other disastrous distortion of the timed plunger operational cycle.
One way such an air leak often occurs is when fragmentary debris, such as fine glass particles, fall into the open piston rod upper end during plunger changeover. The fine particles fall down to the area of the annular seal about the upper end of the air tube and are often picked up by or even embedded in the seal so that repeated cycling causes surface scoring on the tube which will permit the relatively high-pressure cooling air to leak into the relatively low-pressure major chamber of the cylinder. Different types of packing, composite seals and ring combinations have been introduced over the years in an effort to obviate this problem but seal breach, usually due to the presence of undesirable particulant matter, remains a problem at the sliding seal juncture between the fixed air tube and the inside wall of the piston. Manufacturers continue to face the risk of plunger drift and costly down time when it occurs.
Another problem encountered in glass container forming machines of the type heretofore described, is the tendency of the elongated portion of the piston rod because of its length and the distance it must travel in its cycle, to whip-saw slightly relative to the axis of the cylinder in which it is carried. Such action is obviously amplified at the outer tip end of the plunger carried on the rod end. Keeping such a whip-saw action to a minimum requires the use of heavy-duty wide-spaced rings and bushings for supporting the piston and rod in the cylinder.
Still another problem in the type of machine described is the requirement for heavy-duty rings and bushings which bear the brunt of the impacting shock when the plunger and its supporting components move to the maximum down position. Because of the vertical orientation of the cylinder, only a small amount of air pressure is required to start the downward motion and then gravity and inertia contribute to its completion and a shock which must be borne by the rod bushings and rings at the termination of each downward stroke.
The present invention directly addresses the foregoing problems, as will be realized as this specification progresses.